The present invention is related to cooling of airfoils for gas turbine engines and, more particularly, to baffle inserts for impingement cooling of airfoil vanes. Gas turbine engines operate by passing a volume of high energy gases through a series of compressors and turbines in order to produce rotational shaft power. The shaft power is used to turn a turbine for driving a compressor to provide air to a combustion process to generate the high energy gases. Additionally, the shaft power is used to power a secondary turbine to, for example, drive a generator for producing electricity, or to produce high momentum gases for producing thrust. Each compressor and turbine comprises a plurality of stages of vanes and blades, each having an airfoil, with the rotating blades pushing air past the stationary vanes. In general, stators redirect the trajectory of the air coming off the rotors for flow into the next stage. In the compressor, stators convert kinetic energy of moving air into pressure, while, in the turbine, stators accelerate pressurized air to extract kinetic energy.
In order to produce gases having sufficient energy to drive both the compressor and the secondary turbine, it is necessary to compress the air to elevated temperatures and to combust the air, which again increases the temperature. Thus, the vanes and blades are subjected to extremely high temperatures, often times exceeding the melting point of the alloys used to make the airfoils. In particular, the leading edge of an airfoil, which impinges most directly with the heated gases, is heated to the highest temperature along the airfoil. The airfoils are maintained at temperatures below their melting point by, among other things, cooling the airfoils with a supply of relatively cooler air that is typically siphoned from the compressor. The cooling air is directed into the blade or vane to provide cooling of the airfoil through various modes including impingement cooling. Specifically, the cooling air is passed into an interior of the airfoil to remove heat from the alloy. The cooling air is subsequently discharged through cooling holes in the airfoil to pass over the outer surface of the airfoil to prevent the hot gases from contacting the vane or blade. In other configurations, the cooling air is typically directed into a baffle disposed within a vane interior and having a plurality cooling holes. Cooling air from the cooling holes impinges on and flows against an interior surface of the vane before exiting the vane at a trailing edge discharge slot.
The cooling air effectiveness is determined by the distance between the baffle and the airfoil. A greater amount of cooling is provided by increasing the distance to allow a greater volume of airflow. The distance between the baffle and the airfoil is conventionally maintained by a plurality of standoffs that inhibit the baffle from moving and control flow volume. Sometimes only a small volume of airflow is desirable such that the height of the standoffs is difficult or impossible to produce. For example, casting of features onto a surface of an airfoil requires that the feature have a height of about 0.010 inches (˜0.254 mm) or more such that the feature can be reliably measured. Furthermore, machining of features within a cast airfoil is not possible. However, manufacturing tolerances sometimes require that the height be as small as about 0.009 inches (˜0.229 mm) to about 0.005 inches (˜0.127 mm) so that the baffle will fit into the airfoil. These manufacturing restrictions limit the ability to control the airflow, reducing the flexibility with which airfoil durability can be designed. There is, therefore, a need for improving control of airflow between a baffle and an airfoil, particularly when it is desirable to maintain such bodies in close proximity.